This application is based on Japanese Patent Application 2000-242897, filed on Aug. 10, 2000, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to an optical multiplexer/demultiplexer having an arrayed waveguide grating (AWG) and to its manufacture method. More particularly, the present invention relates to an arrayed waveguide grating and its manufacture method in which each core section of some or all arrayed waveguides is made of a combination of a plurality of core regions having a different refraction index.
b) Description of the Related Art
An AWG type optical multiplexer/demultiplexer used in an optical fiber, such as shown in FIG. 18, is known.
The optical multiplexer/demultiplexer shown in FIG. 18 has sixteen channels and is constituted of input waveguides 2(1) to 2(16), a first slab waveguide 3, an arrayed waveguide grating 4, a second slab waveguide 5, and output waveguides 6(1) to 6(16), respectively connected serially and formed on the surface of a substrate 1. The arrayed waveguide grating 4 is constituted of sixteen four arrayed waveguides 6(1) to 6(64) each curved in generally a C-character shape. The arrayed waveguides 6(1) to 6(64) become gradually longer in this order. An optical path length difference between adjacent arrayed waveguides is set to an integer multiplication of a design wavelength (e.g., 1.55 xcexcm).
The slab waveguide 3 receives incidence light from the input waveguides 2(1) to 2(16) at its incidence plane A, and uniformly distributes the light intensity of each incidence light at the incidence plane B of the arrayed waveguides 4(1) to 4(64). A plurality of waveguide is disposed in an arrayed form. The slab waveguide 5 receives incidence light from the arrayed waveguides 4(1) to 4(64) at its incidence plane C, and converges the incidence light on the incidence plane D of the output waveguides 6(1) to 6(16). The convergence points at the incidence plane D are different for respective wavelengths, and the output waveguides 6(1) to 6(16) are disposed in correspondence with the sixteen convergence points.
The signal input/output characteristics of the optical multiplexer/demultiplexer shown in FIG. 18 are as follows. As wavelength multiplexed light having wavelengths xcex1, xcex2, . . . , xcex16 is input to the input waveguide 2(1), light beams having the wavelengths xcex1, xcex2, . . . , xcex16 are output from the output waveguides 6(1), 6(2), . . . , 6(16). As similar wavelength multiplexed light is input to the input waveguide 2(2), light beams having the wavelengths xcex2, xcex3, . . . , xcex1 are output from the output Waveguides 6(1), 6(2), . . . , 6(16). As similar wavelength multiplexed light is input to the input waveguide 2(16), light beams having the wavelengths xcex16, xcex1, . . . , xcex15 are output from the output waveguides 6(1), 6(2), . . . , 6(16). A demultiplexing function and a wavelength routing function are therefore obtained. If the output waveguides 6(1) to 6(16) and the input waveguides 2(1) to 2(16) are interchanged, a multiplexing function is obtained.
With this conventional technology, it is necessary to make the arrayed waveguides 4(1) to 4(64) have different optical path lengths so that each waveguide has the C-character shape and the size reduction of the substrate 1 is difficult. A silicon wafer or the like is scribed into rectangular substrates. If the size of the substrate 1 is large, the number of substrates (optical multiplexers/demultiplexers) capable of being formed from one wafer decreases, which results in an increased cost.
It is an object of the present invention to provide a novel compact AWG type optical multiplexer/demultiplexer and its manufacture method.
According to one aspect of the present invention, there is provided an optical multiplexer/demultiplexer, comprising: a substrate having a principal surface on which the optical multiplexer/demultiplexer is formed; a first waveguide unit having a plurality of first waveguides; a first slab waveguide connected to the first waveguide unit; an arrayed waveguide grating having one end connected to the first slab waveguide, the arrayed waveguide grating including a plurality of arrayed waveguides each having a core section, the core section being a serial connection of a plurality of core regions having a different refraction index, and ratios of lengths of the plurality of core regions having a different refraction index being adjusted so that an optical path length of each of the plurality of arrayed waveguides becomes approximately equal; a second slab waveguide connected to another end of the arrayed waveguide grating; and a second waveguide unit connected to the second slab waveguide and having a plurality of second waveguides.
According to the optical multiplexer/demultiplexer, regardless of that each optical path length of the plurality of arrayed waveguides is made approximately equal, an equiphase plane can be formed on one side of the plurality of arrayed waveguides. Since each of the optical path length of the plurality of arrayed waveguides is made approximately equal, the degree of design freedom for the pattern of the plurality of arrayed waveguides can be increased. Since each of the optical path length of the plurality of arrayed waveguides is made approximately equal, as compared to the case of different optical path lengths, the area occupied by the arrayed waveguide grating can be reduced.
According to another aspect of the present invention, there is provided an optical multiplexer/demultiplexer, comprising: a substrate having a principal surface on which the optical multiplexer/demultiplexer is formed; a first waveguide unit having a plurality of first waveguides; a first slab waveguide connected to the first waveguide unit; an arrayed waveguide grating having one end connected to the first slab waveguide, the arrayed waveguide grating including a plurality of arrayed waveguides each having a core section, the core section being a serial connection of a plurality of core regions having a different refraction index, and ratios of refraction indices of the plurality of core regions having a different refraction index being adjusted so that an optical path length of each of the plurality of arrayed waveguides becomes approximately equal; a second slab waveguide connected to another end of the arrayed waveguide grating; and a second waveguide unit connected to the second slab waveguide and having a plurality of second waveguides.
According to the optical multiplexer/demultiplexer, regardless of that each optical path length of the plurality of arrayed waveguides is made approximately equal, an equiphase plane can be formed on one side of the plurality of arrayed waveguides. Since each of the optical path length of the plurality of arrayed waveguides is made approximately equal, the degree of design freedom for the pattern of the plurality of arrayed waveguides can be increased. As compared to the case of different optical path lengths, the area occupied by the arrayed waveguide grating can be reduced. Since the optical path length of the arrayed waveguide can ba adjusted by the refraction index of the core region, the degree of design freedom for the pattern of the core region can be increased.
According to another aspect of the present invention, there is provided a method of manufacturing an optical multiplexer/demultiplexer having a first waveguide unit, a first slab waveguide, an arrayed waveguide grating, a second slab waveguide, and a second waveguide unit, respectively connected in series, the method comprising: (a) a step of preparing a substrate; (b) a step of depositing a first dad layer on a principal surface of the substrate; (c) a step of forming a first core material layer on the first clad layer, the first core material layer having a first refraction index; (d) a step of changing a partial region of the first core material layer to a second core material layer having a second refraction index different from the first refraction index; and (e) a step of forming an arrayed waveguide grating including a plurality of arrayed waveguides by forming a plurality of core regions including a serial connection of the first and second core material layers in predetermined areas including areas where the first and second core material layers are formed in contact with each other and depositing a second clad layer on the first clad layer, ratios of lengths of the first and second core material layers being adjusted so that an optical path length of each of the plurality of arrayed waveguides becomes approximately equal.
With this manufacture method, the core region is formed by the step of changing the partial region of the first core material layer having the first refraction index to the second core material layer having the second refraction index different from the first refraction index. Accordingly, the structure that each optical path length of the plurality of arrayed waveguides is made approximately equal and the equiphase plane is formed on one side of the arrayed waveguide grating, can be formed with simple steps.
The size of a substrate on which an arrayed waveguide grating is formed can be made small, which results in a compact optical multiplexer/demultiplexer and a low cost. Since a straight arrayed waveguide grating is formed, a light loss to be caused by a curved waveguide can be reduced.
Furthermore, since the refraction index of some core regions among a plurality of core regions is made different for each core section. Accordingly, the degree of design freedom can be improved and a straight arrayed waveguide grating can be formed easily.
Still further, after the second core material layer is formed filling one or more holes formed in the first core material layer, the first and second core material layers are patterned to form a plurality of core sections. In this case, the size and shape of each core section can be controlled easily and the manufacture yield can be improved.